[Python-Dev] Experiment an opt-in new C API for Python? (leave current API unchanged)

[Victor Stinner]

Brett:
> But otherwise I think we are making assumptions here. For me, unless we are trying to trim the C API down to just what is syntactically supported in Python and in such a way that it hides all C-level details I feel like we are guessing at what's best for other VMs, both today and in the future, until they can tell us that e.g. tuple indexing is actually not a problem performance-wise.

The current API of PyTuple_GET_ITEM() allows to write:

   PyObject **items = &PyTuple_GET_ITEM(tuple, 0);

to access PyTupleObject.ob_item. Not only it's possible, but it's used
commonly in the CPython code base. Last week I replaced
&PyTuple_GET_ITEM() pattern with a new _PyTuple_ITEMS() macro which is
private.

To be able to return PyObject**, you have to convert the full tuple
into PyObject* objects which is inefficient if your VM uses something
different (again, PyPy doesn't use PyObject* at all).

More generally, I like to use PyTuple_GET_ITEM() example, just because
it's easy to understand this macro. But it's maybe not a good example
:-)

Victor